\documentclass[tikz, border=10pt]{standalone}
\usepackage[UTF8]{ctex}
\usepackage{tikz}
\newcommand{\iwd}{1000}
\newcommand{\fs}[1]{\fontsize{#1 pt}{0pt}\selectfont}

\begin{document}

\foreach \n in {1, ..., 5} {
    \begin{tikzpicture}[x=1pt, y=1pt]
        \node at (0,0) {\includegraphics[width=\iwd pt]{osi-tcp-\n}};
        % \draw[step=40pt, line width=0.5pt, opacity=0.7, black] (-\iwd/2, -\iwd/2*1.5) grid (\iwd/2, \iwd/2*1.5);
        % \fill [red] (0,0) circle (3pt);
    \end{tikzpicture}
}

\end{document}